1. Field of the Invention
The present invention relates to a bent glass sheet for a vehicle window, especially for an automobile window.
2. Description of the Prior Art
In the field of window glass for vehicles, especially automobiles, there is a large need for bent glass sheets, owing to, among other things, design and aerodynamic considerations. In a first step, the glass sheet is formed into a flat plate, usually by a float process. In a second step, the flat glass sheet is bent. In this second step, first, the glass sheet has to be heated to a temperature near the softening point to make it shapeable. Then, the glass sheet is bent by pressing or self-sagging using a mold with a predetermined shape. When a heated glass sheet is quenched, a compressive layer develops in the surface of the glass sheet. Therefore, after heating and bending the glass sheet in the second step, it is often quenched by blowing air onto it to obtain a bent tempered glass.
A ceramic paste can be printed and baked onto a part of the surface of the bent glass sheet to form a nontransparent layer, which may be esthetically preferable to make the glass fitting portion in, for example, the back window, invisible from the outside. Such a ceramic mask is usually formed as a black frame on the surface of the glass sheet.
Even if the glass sheet is made partially nontransparent, the larger portion of the surface of the bent glass sheet has to be kept transparent to function as a window. The main function of the vehicle window glass is not only to transmit light, but also to convey the situation on the outside accurately to the passengers (especially the driver). Consequently, an improvement of the above second step was to maintain the extremely high smoothness that was obtained by the float process. For example, when a glass sheet is bent and tempered while being suspended with tongs, small tong marks can worsen the appearance of the glass sheet. Methods have been developed to bend and temper a glass sheet without using tongs.
Whether tongs are used or not, strains remain at a peripheral surface portion of the bent glass sheet that are difficult to eliminate completely. These strains can be attributed to the heat history of the glass sheet: The glass sheet has been heated to a temperature near the softening point, and then cooled. In general, the strains due to the heat history remaining at a periphery of a main surface of the glass sheet are minor. However, since the distortion of incident light in the other regions of the bent glass sheet is kept at a very low level, the distortions at a peripheral portion are relatively noticeable. Especially, when a side door window of an automobile is partially open, the distortion of transmitted light (or sometimes reflected light) can be a cause of discomfort to the driver or other passengers.
Therefore, it is an object of the present invention to provide a bent glass sheet for a vehicle window, wherein the discomfort of passengers due to distortion of transmitted light is reduced.
In order to attain this object, a bent glass sheet of the present invention comprises a main surface surrounded by an edge of the bent glass sheet and the main surface has a smooth transparent region. The main surface also has a roughened region that covers at least a portion of a peripheral region of the main surface and in the portion of the peripheral area the roughened region extends at least 3 mm from the edge of the bent glass sheet.
With such a bent glass sheet, the passengers do not feel discomfort due to distortion of transmitted light. If the goal were to simply block transmitted light, it would also be possible to use ceramic masking, which is a well-known technology in the field of automotive window glass making. However, if a part of the surface of the glass sheet is not transparent, it will cause a feeling of uneasiness in the passenger. The above-described bent glass sheet, however, has a roughened surface region, which only scatters incident light.
Throughout this specification, xe2x80x9clightxe2x80x9d means more precisely xe2x80x9cvisible lightxe2x80x9d, as should become clear from the object of the present invention. Consequently, xe2x80x9croughened regionxe2x80x9d means a region having such irregularities that scatter transmitted (or reflected) visible light. Such a roughened region can be formed by roughening a part of a transparent region having a surface that is so smooth that it does not scatter transmitted light. Moreover, xe2x80x9cmain surfacexe2x80x9d means a front/back surface pair of a glass sheet without the edge surface.
The roughened surface region in the bent glass sheet of the present invention is roughened by abrading the transparent region. Often, edge surfaces of vehicle window glasses are abraded. Consequently, the manufacturing steps can be simplified if a portion of the principle surface is roughened by abrading as well.